Compaq 386/20 for Backing Up CHS Disks

[rlerner]

I wanted to keep a bit of a log of what I'm doing with this computer and wanted to put it somewhere where folks might be interested and somebody Googling in the future will find it if they need it.

I had posted recently that I wanted to back up some old IDE disks and some clues on what I can do to access the raw disk data.

The 386 arrived this morning, along with a Gotek floppy emulator and an IDE to SD Card reader as well.



I tore out the drive trays and took a shot of the inside. On the left you can see the clean "eBay" version, and the right what was truly hiding under the drive trays.

Of course an air compressor made quick work of the whole thing but I noticed there's only one IDE channel. I have no idea if this is a 386 thing or what but it did throw me off. So I added a different ribbon cable that can take two drives.

As floppies go, I don't have any 5.25 laying around right now, and very few 3.5. The Compaq connectors were a bit different from my floppy emulator's:


The bottom edge connector is the 5.25, the middle is the Compaq 3.5, and the top one is the Gotek. Thankfully, being a hoarder, I found the correct ribbon cable for the Compaq to interface with the Gotek -- but the machine I have also didn't have the floppy power connector. I tried to run without it, the display lit up but I couldn't change disks with the numbers and it didn't see any disks.

I found a molex to floppy, added that, plugged it in and it started working. I used the tinyurl link in the description of this video to get the tool I needed to correctly format the data on the USB stick.

I then learned that Compaq 386's don't have an onboard BIOS utility, you had to use a diskette. Thankfully, archive.org had a copy and I was able to get the time and date to be something closer than 01/01/1980. But the clock would drift something awful, and it wouldn't remember the drive type I put in and kept saying it needs the diagnostic disk.

I figured the CMOS battery took a dump and went to go pop that out and replace it, when I remembered that you can't just do that with one of these machines. I pulled the RTC chip and started googling, hoping I could find an easy drop in solution. While there are a few on Github that would require me to order a board, source components, and build it myself there was another way I came across.




In these pin locations, you can drill or file down until you hit metal, then solder on some wires to a CR2032 battery holder, which I did:



And so far, I was able to install MS-DOS 6.22 and I started to install the OEM Compaq 3.1 until the drive started to fail :/... Going to look into this IDE SD Card thing and report back.

 

[Plasma]

Mmmm dusty. Before ATAPI CD-ROM drives were widespread, it was common to only have one IDE channel integrated on the motherboard.

I assume you are aware of the 32MB hard drive size limit with DOS 3.1...

 

[T-R-A]

And a lot of older Compaqs didn't have a "user-defined" type for drive support in the older BIOS settings (also set from floppy), so your options on HDDs may be limited.

 

[rlerner]

Mmmm dusty. Before ATAPI CD-ROM drives were widespread, it was common to only have one IDE channel integrated on the motherboard.

I assume you are aware of the 32MB hard drive size limit with DOS 3.1...

Sorry! OEM Compaq Windows 3.1! I wasn't aware of that limitation, however. My first DOS was 5.0.

And a lot of older Compaqs didn't have a "user-defined" type for drive support in the older BIOS settings (also set from floppy), so your options on HDDs may be limited.

Yeah I'm finding that out. I've heard a few things about XTide, a custom BIOS but I'm not sure what kind of a time I'll have with that since it appears to be a bit different from the EEPROMs I'm used to.

 

[dhamilton]

I love these Compaq computers, I have one. That being said, you couldn't have picked a worse computer to use as a test-bed for IDE disks. This computer has what at the time was referred to as a "Winchester" hard drive interface. Is it IDE? Yes. Is it the IDE you're familiar with? Not quite.

Compaq offering what would eventually become IDE all the way back in 1987. But back then it was referred to as "Winchester" and it was much simpler and specific. Like someone said below, this is back in a time with MFM and ESDI drives were quite common, and the use of "Drive Types" was the thing. IDE used this same scheme back then. There were only a hand-full of different options for these drives, so the drive type tables had specifically which drive you had. There was no "auto-detect geometry" option.

So, with this computer everything is specific to what Compaq sold at the time. You can't just slap any disk in the computer and be able to test it, unfortunately.

Your best bet for a disk test rig is a late 90s Pentium II or III clone system. Those things give you maximum flexibility. You can mount up a 1987 Winchester or a 1997 20 GB drive in one of those systems.

 

[rlerner]

I may end up cleaning this up now that I got it fixed and tested it and just trying to resell it. I'd like to keep it but the idea was to downsize the amount of stuff I've held onto for years and another tower sadly isn't going to be the solution for this.

Several of my drives I have do follow the "Type" specs -- my father had worked at a place back then that used exclusively Compaq and so anything they discarded would end up at my house, so most of my stuff has "Compaq Spare #" on them.

That said, some don't and my SD Card + IDE thing isn't working out yet and I'm not sure how to make it act like these older geometries, so keeping it to play Keen and Bio Menace is probably moot as well.

 

[rlerner]

@dhamilton : I have a Dell Poweredge 2300 laying around, which fits the definition of a Pentium 3 but it does NOT have built in IDE, it has floppy and it has SCSI (since it is a server). My reasoning behind getting the Compaq was something that was old enough where I could specify C/H/S. Compaq being a mistake for that, I likewise assume this SCSI box's bios has no way of working with it.

Or will that matter with a PCI-based IDE card?

 

[ohmylove2u]

Some complex system circuit boards are made up of several layers.
Removing parts from PCB may damage scallop hole.
Be careful！

 

[rlerner]

Some complex system circuit boards are made up of several layers.
Removing parts from PCB may damage scallop hole.
Be careful！

Are you talking about where I carved the side of that RTC? I had watched a ton of videos and looked at ones where people carved it down, there was no way I was going to hit anything behind it. I was a bit nervous about it but I was able to read 0.5vDC from the metal I did hit, so it seemed safe enough to throw 3v and look for smoke.

 

[modem7]

Are you talking about where I carved the side of that RTC? I had watched a ton of videos and looked at ones where people carved it down, there was no way I was going to hit anything behind it. I was a bit nervous about it but I was able to read 0.5vDC from the metal I did hit, so it seemed safe enough to throw 3v and look for smoke.

We had someone here not realise that the procedure included disconnection of the internal battery. So what happened is that the 3V external battery got put in parallel with the very low internal battery. The low internal battery dragged down the 3V down to something much lower.

 

[ohmylove2u]

Are you talking about where I carved the side of that RTC? I had watched a ton of videos and looked at ones where people carved it down, there was no way I was going to hit anything behind it. I was a bit nervous about it but I was able to read 0.5vDC from the metal I did hit, so it seemed safe enough to throw 3v and look for smoke.

I mean, is it possible that soldering the RTC chip out&on caused harm to the mainboard？

 

[rlerner]

I mean, is it possible that soldering the RTC chip out&on caused harm to the mainboard？

The RTC is socketed, I took the chip out and did it on my desk (Filing, soldering) and then put it back in. Mainboard wasn't effected at all.

We had someone here not realise that the procedure included disconnection of the internal battery. So what happened is that the 3V external battery got put in parallel with the very low internal battery. The low internal battery dragged down the 3V down to something much lower.

First I'm seeing about something needing to be disconnected, worst comes to worst I could always replace it with one of these if the voltage drops or it doesn't last like I'd like.

 

[Caluser2000]

Mmmm dusty. Before ATAPI CD-ROM drives were widespread, it was common to only have one IDE channel integrated on the motherboard.

I assume you are aware of the 32MB hard drive size limit with DOS 3.1...

Yeah. That was the reason I chose a pirated copy of Compaq MS Dos 3.31 for my brand new 286/16 clone system with 40mb ide hdd then bought a retail copy of DRDos 6.0.

 

[modem7]

We had someone here not realise that the procedure included disconnection of the internal battery. So what happened is that the 3V external battery got put in parallel with the very low internal battery. The low internal battery dragged down the 3V down to something much lower.

First I'm seeing about something needing to be disconnected, worst comes to worst I could always replace it with one of these if the voltage drops or it doesn't last like I'd like.

Just be aware that there are no guarantees.

First, notice that, "Drop-In replacement for Dallas DS12887" contains DS12887, not DS1287.

Notice that, "This part should be compatible with following RTC modules:" contains "should be", not "is". There is a reason for that. Because it may not work in some circumstances. More information at [here].

 

[Krille]

Yeah I'm finding that out. I've heard a few things about XTide, a custom BIOS but I'm not sure what kind of a time I'll have with that since it appears to be a bit different from the EEPROMs I'm used to.

Everything you need is here. Do not use the old versions from Google Code.

 

[dhamilton]

@dhamilton : I have a Dell Poweredge 2300 laying around, which fits the definition of a Pentium 3 but it does NOT have built in IDE, it has floppy and it has SCSI (since it is a server). My reasoning behind getting the Compaq was something that was old enough where I could specify C/H/S. Compaq being a mistake for that, I likewise assume this SCSI box's bios has no way of working with it.

Or will that matter with a PCI-based IDE card?

There are some IDE controllers that have their own BIOS for setup, kind of like an Adaptec SCSI card. I can't recall what brands they were.

Your best bet is to find a junker on a local Facebook group or something that just has all the stuff built in. If you find basically any run of the mill late 90s clone, it'll probably have an AWARD BIOS (v4.51) more than likely, and with those things you can do anything you want. It lets you pick any mode and enter any parameters for your hard disks.



It's easy to fall into the pit of buying parts and getting in deeper, finding yourself researching and learning about things you never ever wanted to just to get something simple working.

 

[rlerner]

Lol, yeah I'm cleaning up this 386 and I'm just going to try and recover my costs on it at this point. I'll be happy knowing I was able to keep a machine like this going and that somebody who wants it will have it.

Going to have to park this project until I see a Pentium unit around